The invention relates generally to the field of two wire sensor devices, and in particular to a two-wire sensor device with a measuring sensor that has two connections for transmitting the measurement signal and simultaneously providing electrical power.
Conventional two-wire sensors comprise a measuring sensor that measures a physical quantity (e.g., temperature, pressure, or magnetic field strength) and electronic components to process the signals provided by the measuring sensor. Electrical power and the measured and processed signals are conducted over only two lines, which is the basis of the name two-wire sensor. Consequently, a two-wire sensor has only two connections, which simultaneously are used to supply both electrical power and to conduct the measured and processed signals.
Conventional two-wire sensors have the properties of switched current sources. Therefore, they can be connected only in parallel. Consequently, four lines are required to interconnect two two-wire sensors that are located at different places. If n two-wire sensors located at different places are connected in parallel, two n cable strands and an additional 4nxe2x88x922 plugs are required. A disadvantage of these two-wire sensors is that many lines are required when several sensors are connected in parallel.
Therefore, there is a need for a two wire sensor capable of being connected in series with another two wire sensor.
Briefly, according to the present invention, an end stage is responsive to the two connections from a measuring sensor and provides a voltage signal indicative thereof, which, during operation of the measuring device is always greater than an adjustable reference voltage signal and whose amplitude is a measure of the physical quantity sensed by the measuring sensor.
The two-wire sensor of the present invention has the property of a voltage source, rather than a current source. Consequently, a plurality of the inventive two-wire sensors can be connected in series. A series connection with n two-wire sensors requires n+1 lines and 2n plugs, while a parallel connection requires 2n lines and 4nxe2x88x922 plugs, which is twice as many components, if n greater than 1.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.